/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

/*
 * Source:
 * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/extra/AtomicDoubleArray.java?revision=1.5
 * (Modified to adapt to guava coding conventions and
 * to use AtomicLongArray instead of sun.misc.Unsafe)
 */

package com.google.common.util.concurrent;

import static java.lang.Double.doubleToRawLongBits;
import static java.lang.Double.longBitsToDouble;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.primitives.ImmutableLongArray;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.util.concurrent.atomic.AtomicLongArray;

/**
 * A {@code double} array in which elements may be updated atomically. See the {@link
 * java.util.concurrent.atomic} package specification for description of the properties of atomic
 * variables.
 *
 * <p><a id="bitEquals"></a>This class compares primitive {@code double} values in methods such as
 * {@link #compareAndSet} by comparing their bitwise representation using {@link
 * Double#doubleToRawLongBits}, which differs from both the primitive double {@code ==} operator and
 * from {@link Double#equals}, as if implemented by:
 *
 * <pre>{@code
 * static boolean bitEquals(double x, double y) {
 *   long xBits = Double.doubleToRawLongBits(x);
 *   long yBits = Double.doubleToRawLongBits(y);
 *   return xBits == yBits;
 * }
 * }</pre>
 *
 * @author Doug Lea
 * @author Martin Buchholz
 * @since 11.0
 */
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public class AtomicDoubleArray implements java.io.Serializable
{
    private static final long serialVersionUID = 0L;

    // Making this non-final is the lesser evil according to Effective
    // Java 2nd Edition Item 76: Write readObject methods defensively.
    private transient AtomicLongArray longs;

    /**
     * Creates a new {@code AtomicDoubleArray} of the given length, with all elements initially zero.
     *
     * @param length the length of the array
     */
    public AtomicDoubleArray(int length)
    {
        this.longs = new AtomicLongArray(length);
    }

    /**
     * Creates a new {@code AtomicDoubleArray} with the same length as, and all elements copied from,
     * the given array.
     *
     * @param array the array to copy elements from
     * @throws NullPointerException if array is null
     */
    public AtomicDoubleArray(double[] array)
    {
        int len = array.length;
        long[] longArray = new long[len];
        for (int i = 0; i < len; i++)
        {
            longArray[i] = doubleToRawLongBits(array[i]);
        }
        this.longs = new AtomicLongArray(longArray);
    }

    /**
     * Returns the length of the array.
     *
     * @return the length of the array
     */
    public final int length()
    {
        return longs.length();
    }

    /**
     * Gets the current value at position {@code i}.
     *
     * @param i the index
     * @return the current value
     */
    public final double get(int i)
    {
        return longBitsToDouble(longs.get(i));
    }

    /**
     * Atomically sets the element at position {@code i} to the given value.
     *
     * @param i        the index
     * @param newValue the new value
     */
    public final void set(int i, double newValue)
    {
        long next = doubleToRawLongBits(newValue);
        longs.set(i, next);
    }

    /**
     * Eventually sets the element at position {@code i} to the given value.
     *
     * @param i        the index
     * @param newValue the new value
     */
    public final void lazySet(int i, double newValue)
    {
        long next = doubleToRawLongBits(newValue);
        longs.lazySet(i, next);
    }

    /**
     * Atomically sets the element at position {@code i} to the given value and returns the old value.
     *
     * @param i        the index
     * @param newValue the new value
     * @return the previous value
     */
    public final double getAndSet(int i, double newValue)
    {
        long next = doubleToRawLongBits(newValue);
        return longBitsToDouble(longs.getAndSet(i, next));
    }

    /**
     * Atomically sets the element at position {@code i} to the given updated value if the current
     * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
     *
     * @param i      the index
     * @param expect the expected value
     * @param update the new value
     * @return true if successful. False return indicates that the actual value was not equal to the
     * expected value.
     */
    public final boolean compareAndSet(int i, double expect, double update)
    {
        return longs.compareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
    }

    /**
     * Atomically sets the element at position {@code i} to the given updated value if the current
     * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
     *
     * <p>May <a
     * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
     * fail spuriously</a> and does not provide ordering guarantees, so is only rarely an appropriate
     * alternative to {@code compareAndSet}.
     *
     * @param i      the index
     * @param expect the expected value
     * @param update the new value
     * @return true if successful
     */
    public final boolean weakCompareAndSet(int i, double expect, double update)
    {
        return longs.weakCompareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
    }

    /**
     * Atomically adds the given value to the element at index {@code i}.
     *
     * @param i     the index
     * @param delta the value to add
     * @return the previous value
     */
    @CanIgnoreReturnValue
    public final double getAndAdd(int i, double delta)
    {
        while (true)
        {
            long current = longs.get(i);
            double currentVal = longBitsToDouble(current);
            double nextVal = currentVal + delta;
            long next = doubleToRawLongBits(nextVal);
            if (longs.compareAndSet(i, current, next))
            {
                return currentVal;
            }
        }
    }

    /**
     * Atomically adds the given value to the element at index {@code i}.
     *
     * @param i     the index
     * @param delta the value to add
     * @return the updated value
     */
    @CanIgnoreReturnValue
    public double addAndGet(int i, double delta)
    {
        while (true)
        {
            long current = longs.get(i);
            double currentVal = longBitsToDouble(current);
            double nextVal = currentVal + delta;
            long next = doubleToRawLongBits(nextVal);
            if (longs.compareAndSet(i, current, next))
            {
                return nextVal;
            }
        }
    }

    /**
     * Returns the String representation of the current values of array.
     *
     * @return the String representation of the current values of array
     */
    @Override
    public String toString()
    {
        int iMax = length() - 1;
        if (iMax == -1)
        {
            return "[]";
        }

        // Double.toString(Math.PI).length() == 17
        StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
        b.append('[');
        for (int i = 0; ; i++)
        {
            b.append(longBitsToDouble(longs.get(i)));
            if (i == iMax)
            {
                return b.append(']').toString();
            }
            b.append(',').append(' ');
        }
    }

    /**
     * Saves the state to a stream (that is, serializes it).
     *
     * @serialData The length of the array is emitted (int), followed by all of its elements (each a
     * {@code double}) in the proper order.
     */
    private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException
    {
        s.defaultWriteObject();

        // Write out array length
        int length = length();
        s.writeInt(length);

        // Write out all elements in the proper order.
        for (int i = 0; i < length; i++)
        {
            s.writeDouble(get(i));
        }
    }

    /**
     * Reconstitutes the instance from a stream (that is, deserializes it).
     */
    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException
    {
        s.defaultReadObject();

        int length = s.readInt();
        ImmutableLongArray.Builder builder = ImmutableLongArray.builder();
        for (int i = 0; i < length; i++)
        {
            builder.add(doubleToRawLongBits(s.readDouble()));
        }
        this.longs = new AtomicLongArray(builder.build().toArray());
    }
}
